Microsoft Security Bulletin (MS99-048)

--------------------------------------



Patch Available for "Active Setup Control" Vulnerability

Originally Posted: November 11, 1999



Summary

=======

Microsoft has released a patch that eliminates a vulnerability that could

allow a malicious user to embed an unsafe executable within an email and

disguise it as a safe type of attachment. Through a complicated series of

steps, the unsafe executable could be made to execute under certain

conditions, if the user opened the attachment.



Frequently asked questions regarding this vulnerability can be found at

http://www.microsoft.com/security/bulletins/MS99-048faq.asp.



Issue

=====

A particular ActiveX control allows cabinet files to be launched and

executed. This could allow an HTML mail to contain a malicious

cabinet file, disguised as a file of an innocuous type. If a user

attempted to open this file, the operation would fail but could,

depending on the mail package, leave a copy of the file in a known

location. The ActiveX control could then be used via a script

embedded in the mail to launch the copy, thereby executing the

malicious code.



The vulnerability could only be exploited in cases where a mail reader were

used that allowed scripts in HTML mail and stored temporary copies of

launched programs in known locations. The patch restricts the ability of

the control to launch unsigned cabinet files that have been downloaded

from the local machine.



Affected Software Versions

==========================

The affected ActiveX control ships as part of Microsoft Internet Explorer 4

and 5



Patch Availability

==================

 - http://windowsupdate.microsoft.com

 - http://www.microsoft.com/msdownload

 - http://www.microsoft.com/msdownload/iebuild/ascontrol/en/ascontrol.htm



NOTE: Microsoft produces security patches for Internet Explorer 4.01 SP2

and higher. In the event that this package is applied to Internet Explorer

4.01  SP1, the package states that a fix is not needed. This message is

incorrect, as the vulnerability does exist on Internet Explorer 4.01 SP1.

If you are using Internet Explorer 4.01 SP1, please upgrade to the latest

version of Internet Explorer to resolve this issue.



More Information

================

Please see the following references for more information related to this

issue.

 - Microsoft Security Bulletin MS99-048: Frequently Asked Questions,

   http://www.microsoft.com/security/bulletins/MS99-048faq.asp

 - Microsoft Knowledge Base (KB) article Q244540, Update Available

   for "Active Setup Control" Vulnerability,

   http://support.microsoft.com/support/kb/articles/q244/5/40.asp

   (Note: It may take 24 hours from the original posting of this

   bulletin for the KB article to be visible.)

 - Microsoft Security Advisor web site,

   http://www.microsoft.com/security/default.asp.



Obtaining Support on this Issue

===============================

This is a fully supported patch. Information on contacting Microsoft

Technical Support is available at

http://support.microsoft.com/support/contact/default.asp.



Acknowledgments

===============

Microsoft acknowledges Juan Carlos Garcia Cuartango of Spain for

bringing this issue to our attention.



Revisions

=========

 - November 11, 1999: Bulletin Created.



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